Imaging devices form images on image receiving surfaces that include paper and other print media. Different imaging or printing techniques, which include laser printing, inkjet printing, offset printing, dye-sublimation printing, thermal printing, and the like, may be used to produce printed documents. In particular, inkjet imaging devices eject liquid ink from printheads to form images on an image receiving surface. The image receiving surface may be a media substrate or an intermediate imaging member. The image on the intermediate imaging member is later transferred to media substrate. Once the ejected ink is on the image receiving surface, the ink droplets quickly solidify to form an image. A media transport system transports the media substrate along a media transport path from supply sources to the printheads or intermediate imaging member and then to subsequent stations for further processing, such as sheet output collation, finishing, and the like.
In many imaging devices, the media substrate is inverted and an image is formed on the reverse side of the substrate to generate a duplex or two-sided document. To perform such inversion, the media transport system includes an inverter for reversing the orientation of the media substrate and a duplex loop for returning the inverted media substrate to the printheads or the intermediate imaging member. An inverter typically includes an entrance path leading to a sheet driver, such as nip formed between a pair of rollers. The sheet driver draws the sheet from the entrance path into a reversing chute, reverses the direction of the sheet, and drives the sheet out of the reversing chute into the duplex loop for subsequent imaging of the non-imaged side.
As the process speeds of imaging devices generally become faster, duplex printing using these devices requires the sheets entering the inverter to be rapidly accelerated from the process speed to a much higher inverter speed. For example, in many high-speed imaging devices using a single inverter, the sheets are accelerated in a very short distance from a process to an inverter speed that is approximately twice the process speed for movement into the inverter. After the sheets enter the inverter, the sheets are rapidly decelerated from the higher inverter speed to a stop and then rapidly re-accelerated to the inverter speed for exiting from the inverter. The increased sheet velocities and accelerations required for inversion can damage the sheets and cause jams along the media transport path. Moreover, images produced using inkjet imaging devices are more sensitive to abuse than images produced using xerographic imaging devices, such as laser printers.
Some imaging devices implement a dual inverter system of two independent but cooperative sheet inverters to reduce the sheet velocities and accelerations needed to perform duplex printing at high process speeds. In these devices, the two inverters are sheet control gated to receive alternate sheets from the sheet path for inversion in the inverters. The dual inverters may operate at substantially the same sheet velocity as the sheet path instead of the much higher speed and acceleration/deceleration typical of conventional single inverter systems. However, adding multiple inverters along the media transport system increases the number of components needed to perform sheet inversion and the complexity of the system required to maintain proper sequencing of the inverted sheets. Accordingly, improvements to imaging devices that enable high-volume, high-speed sheet inversion with reduced inverter components and complexity would be beneficial.